In various fields including manufacture of semiconductor devices and liquid crystal displays, positive or negative working photoresists have been used for fine processing or patterning. As such photoresists, there are conventionally known a positive working radiation sensitive composition comprising a novolak resin and a quinone diazide photosensitizer, a chemically amplified positive or negative working radiation sensitive composition, and a negative working resist such as a polyvinyl cinnamate-based radiation sensitive composition, a bisazide-rubber-based radiation sensitive composition, and a photopolymerization type radiation sensitive composition, etc. In such photoresists, there are required various characteristics depending on their intended use. For example, in processing of semiconductor devices, there are required characteristics such as high sensitivity, high resolution and etching resistance.
On the other hand, various patterned films including an inter-layer dielectric have been used in semiconductor devices, liquid crystal displays, printed circuit substrates, etc. These patterned film is formed generally by applying film-forming organic or inorganic materials or depositing these materials from a gaseous phase to form a coating and then etching the coating through a patterned photoresist. If there is necessity for forming a fine pattern by this etching, gaseous etching is generally used. However, the gaseous etching is problematic because an apparatus used is expensive and the rate of processing is low.
Further, in the production step of semiconductor devices or the like (e.g. a vapor deposition step of wire by CVD), the devices are exposed to high temperatures at higher than 400° C. Accordingly, when organic materials are used as an inter-layer dielectric in the devices exposed to such high temperatures, it can not be opposed satisfactorily in respect of heat resistance. Because of this, the use of inorganic materials is desired as the materials such as an inter-layer dielectric. As the inorganic materials, silica type ceramic films are often used by the reason why it has superior not only in heat resistance but also in abrasion resistance, corrosion resistance, insulating properties, transparency, etc.
Conventionally, such patterned silica type ceramic film is formed generally by etching of a ceramic film using a patterned photoresist as an etching mask, and is economically problematic. Accordingly, there is a demand for a method of forming a finely patterned inter-layer dielectric without using gaseous etching.
For this demand, a method of forming a ceramic film pattern is proposed which comprises applying a radiation sensitive polysilazane composition to form a radiation sensitive polysilazane coating film, exposing and developing the coating film to form a patterned polysilazane film, converting the patterned polysilazane film into a silica type ceramic film. For example, JP-A 5-88373 describes a method of forming a ceramic film pattern which comprises applying a polysilazane-containing coating solution onto a substrate to form a coating film thereon, patternwise irradiating the coating film with UV rays in an oxidizing atmosphere to cure the portion exposed to UV rays, removing a portion not exposed to UV rays, and converting the patterned polysilazane film into a silica type ceramic film. The polysilazane-containing coating solution described above can be regarded as a negative working photoresist because the exposed portion cures and remains after development.
On the other hand, fine processing of semiconductor devices or the like is advancing. As a result, a positive working material, as a resist, with high resolution and high etching resistance such as oxygen plasma resistance is desired. Further, when the patterned coating is used as a remaining inter-layer dielectric, it is desired that the coating materials satisfy not only the aforementioned requirements for fine processing but also excellent properties such as high heat resistance, low dielectric constant and transparency required for the inter-layer dielectric. For these demands, the present inventors proposed a positive working radiation sensitive polysilazane composition comprising a polysilazane and a photo acid generator; a method of forming a patterned polysilazane film which comprises applying said radiation sensitive polysilazane composition to form a coating film, patternwise irradiating the coating film, dissolving and removing the irradiated part of the coating film to form a patterned polysilazane film; and a method of forming a patterned insulating film which comprises leaving said patterned polysilazane film in the ambient atmosphere or burning the film thereby converting it into a silica type ceramic film in Japanese Patent Application No. Hei 11-283106 (JP-A 2000-181069).
In addition, the present inventors proposed a positive working radiation sensitive polysilazane composition having improved storage stability by use of a modified poly(sil sesquiazane) in Japanese Patent Application No. Hei 12-108023.
In the method of using these positive working radiation sensitive polysilazane compositions, an acid is formed in the light-exposed portion of the radiation sensitive polysilazane coating film. By the acid formed, Si—N linkages in the polysilazane are cleaved and then react with H2O molecules to form silanol (Si—OH) linkages, whereby decomposition of the polysilazane occurs. In these prior art techniques, however, the treatment method described specifically as a method of decomposing the polysilazane is a method of bringing the exposed radiation sensitive polysilazane film into contact with water.
These proposed positive working radiation sensitive polysilazane compositions have higher, resolution than that of the negative working radiation sensitive polysilazane compositions, but it is necessary to improve the resolution in order to cope with fine patterning. Further, the light-exposed radiation sensitive polysilazane composition is contacted with water to decompose the polysilazane. Possibly because the decomposition of the polysilazane proceeds only in the vicinity of the surface of the film of the radiation sensitive polysilazane composition, the coating film in the exposed portion is not sufficiently removed under some decomposition conditions by subsequent development with an aqueous alkali solution, and development residues may remain on the pattern after development. In addition, there is another problem that the adhesion of the radiation sensitive polysilazane coating film to the substrate is not sufficient. Accordingly, a method of decomposing a radiation sensitive polysilazane film free of aforementioned problems is also regarded. Further, when the radiation sensitive polysilazane coating film is converted by burning into a silica type ceramic film, oxidation of the polysilazane does not sufficiently proceed by merely heating the polysilazane coating film. As a consequence of this, the resultant silica type ceramic film has a large number of Si—N linkages of polysilazane in the coating film, thus making it difficult to form a film having a sufficiently low dielectric constant required for an inter-layer dielectric. There is a further problem that when a large number of Si—N linkages remain in the silica type ceramic film, the film easily absorbs moisture to form a film having unstable physical properties. Accordingly, when burning the radiation sensitive polysilazane coating film, a method of burning a radiation sensitive polysilazane coating film is also demanded, wherein the polysilazane in the coating film can be converted easily and sufficiently into silica type ceramic film and give a silica type ceramic film excellent in characteristics such as dielectric constant and free of residual Si—N linkages in the film.
In view of these circumstances, an object of this invention is to provide a method of forming a patterned polysilazane coating by use of a radiation sensitive polysilazane composition, wherein the polysilazane in the radiation sensitive polysilazane composition after exposure can be decomposed in a short time to give a patterned polysilazane film excellent in adhesion to a substrate and free of development residues on the pattern after development.
Further, an object of this invention is to provide a method of burning a radiation sensitive polysilazane coating film wherein oxidation of the polysilazane sufficiently proceeds even by simple heating so that no or few Si—N linkages exist in the film.
Further, an object of this invention is to provide a radiation sensitive polysilazane composition, a method of forming a patterned radiation sensitive polysilazane coating, and a method of burning a radiation sensitive polysilazane coating film, wherein a silica type ceramic film with a low dielectric constant, excellent in heat resistance, abrasion resistance, corrosion resistance, insulating properties and transparency and useful as an inter-layer dielectric can be formed.
Further, an object of this invention is to provide a radiation sensitive polysilazane composition having high resolution.
The present inventors made extensive study for achieving these objects, and as a result, obtained the following knowledge. That is, when forming a patterned polysilazane film by use of a positive working radiation sensitive composition such as a radiation sensitive polysilazane composition comprising a polysilazane and a photo acid generator, the polysilazane can be decomposed in a short time, and development residues do not remain on the pattern after development by contacting the exposed radiation sensitive polysilazane coating film with a water vapor-containing gas, that is, subjecting to moistening treatment; the decomposition time can be further reduced by increasing the content of water vapor in the gas used or by heating the radiation sensitive polysilazane coating film at the time of moistening treatment; the partial pressure of water vapor in the atmosphere for moistening treatment can be further increased by relaxation of the conditions of moisture condensation on the surface of the film in heating the film, whereby the time required for decomposition of the polysilazane can be further reduced; and the adhesion of the polysilazane coating film to the substrate is also improved by heating during development.
Further, the present inventors found that when the radiation sensitive polysilazane coating film is burned, conversion of the coating film into silica type ceramic film can be conducted easily and sufficiently by exposing the coating film and subjecting the resultant film to the moistening treatment before burning, to give a silica type ceramic film excellent in properties and free of Si—N linkages therein.
Further, the present inventors found that resolution can be increased by adding a water-soluble compound as a shape stabilizer to the radiation sensitive composition comprising a specific modified poly(sil sesquiazane) and a photo acid generator, and this radiation sensitive composition can form a finely patterned inter-layer dielectric excellent in dielectric constant, insulating properties and mechanical properties after burning.
This invention is based on these findings.